No, the tank isn't re-cycling, what's happening is that your tank is being over loaded with nutrients that your filtration system can't cope with. Ammonia is usually due to the rotting of old food and waste in an aquarium, this can also include the rotting of plants, but in an established filter system, the "good bacteria" almost turns the ammonia into less harmful nitrite but more of it. This is the most common problem in new aquariums. In a healthy aquarium however, the nitrite is then again converted into even less harmful nitrate which is relatively safe provided that it isn't allowed to build up. Whether it is ammonia, nitrite, or nitrate which is causing the problem, they can all be reduced by doing a partial water change, however, it looks as if in your tank there is so much waste, your filter bacteria just can't cope and so the rotting food and waste can't be converted into its less harmful states. Doing a 50% water change will have no effect on the ammonia levels if there are bits of food and waste lieing around the tank because as soon as you remove the old ammonia, new ammonia starts to form again from the decaying food. Make sure that when doing water changes, all food and waste is removed before it has the chance of turning from harmless protein into harmful ammonia and nitrites. I.E, remove any food the fish have ignored asap.
I hope we can solve your problem, and if in doubt, give us a shout. 
__________________
If you have a big enough tank with enough hiding places, pH of around 7, you can keep virtually any fish together as long as all the fish are around the same size and these two groups of fish are avioded:
Serrasalmus
Tetradon(figure eights and dwarfs are the
exception).
I keep a successful community of fish in a 4 foot tank including the following families:
Cichlids, tetras, loaches, gouramis, barbs, rainbows, livebearers, killiefish, catfish, puffers.
|